I dug out my old iPAQ for this purpose. It's got all the features that I need and a good screen. Plus, since I already own it, it's no extra cost! However, the problem I found (and a warning for others) is that the battery was dead and wouldn't take a charge. The model I have (3835) has batteries that aren't easily replaceable and the licensed replacements are WAY too expensive. Fortunately ebay has some for cheap, so I'm buying one there.
Anyway, if you want to go the PDA route, there are lots of apps that can help. I'm not sure how active the iTouch homebrew area is, so there might be some good stuff there too.